Determination of the Critical Rate and Water Coning Height in Naturally Fractured Reservoirs
Research output: Research › Master's Thesis
The work presents an improved version of the method of Birks (1963) to predict water coning behaviour in naturally fractured reservoirs, operated under bottom water drive. Birks’ method assumes a general, empirically derived, fixed critical boundary radius. The method underestimates the critical rate of water-free production. The author of this thesis found that the critical boundary radius is a function of the effective drawdown, depending on the flowrate, fluid and reservoir flow properties, rather than a fixed value. With the actual modification the estimated rate limits seem to be more realistic. Based on field measurements including FMI and drawdown data, a design of a workflow suitable for derivation of input data for the use in the modified critical rate calculation model was derived. The input parameters pertain to data required for calculation of the laminar flow factor A, which is the inverse of the productivity index, the turbulence flow factor B and the inclination angle θ of the unique equivalent fracture. The applicability of the designed workflow for preparation of input data was demonstrated, resulting in calculation of the water cone height, deploying the modified model. It is concluded that the derived model achieves reasonable results, however, it is recommended to apply the model on more field cases with measured water cone heights in order to verify the approach. The Master thesis was initiated by the Norwegian company DNO ASA, in order to evaluate the water-free critical rate associated with water coning at their Tawke Field in the Middle East. Data including drawdown, FMI, PVT as well as production rates and pressures were provided.