Uncertainty Assessment in the Prediction of Recovery Factor from Water Drive Gas Reservoirs

Capital investment in the petroleum industry had been constantly faced with the risk due to uncertainties in the prediction of reservoir performance. So investors need accurate estimates of the uncertainties to reduce the investment risk in this industry. Statistical methods of risk analysis in petroleum industry are faced with limitations because of various assumptions. In this paper, uncertainty of gas recovery factor from water drive gas reservoirs will be investigated using four different methods including: (1) experimental design theory and response surface methodology, (2) multiple realization tree, (3) relative variation factor and finally (4) integrated mismatch method. This study shows that the greatest uncertainty in estimating the gas recovery factor of these reservoirs is associated with reservoir permeability, wellhead pressure, aquifer permeability and tubing diameter and therefore by reducing the uncertainty in the calculation of these four factors, investment risk can be reduced. Also a multiple realization tree method has high accuracy (relative error less than 3%) with respect to the other three methods in estimation of most probable valve of gas recovery factor.