Abstrac tReservoir simulation is routinely employed in the prediction of reservoir performance under different depletion and operating scenarios . Usually, a single history matched model, conditioned to production data, is obtained . The model is then used to forecast fotore production profiles . Since the history match is non-unique, this is essentially an inverse problem. Hence the forecast production profiles are uncertain, although this uncertainty is not usually quantified .This paper presents a new approach for generating uncertain reservoir performance predictions and quantifying the uncertainty associated with forecasting fotore performance . Firstly, we generate multiple reservoir realizations using a new stochastic algorithm . This involves adaptively sampling the model parameter space using an algorithm, which biases the sampling towards regions of good fit . Using the complete ensemble of models generated, we resample from the posterior distribution and quantify the uncertainty associated with forecasting reservoir performance, in a Bayesian framework .To demonstrate the strength of the method in performance prediction, we use an upscaled model to history match fine scale data . We then forecast the fine grid performance using the maximum likelihood model and quantify the uncertainty associated with the predictions . We demonstrate that the maximum likelihood model is highly accurate in reservoir performance prediction .This method differs from other methods for generating multiple reservoir realizations in the following way . Rather than seeking a single global optimum, the algorithm selectively samples parameter space to derive an ensemble of models . These models share the common property of fitting the observed data to some degree of accuracy . This approach is reasonable since the inverse problem is ill-posed . In contrast to other stochastic methods, the algorithm performs a guided search in parameter space by using information derived from the complete ensemble of previously generated models . Hence no external directionality is imposed on the search process .In Bayesian analysis, the posterior probability distribution characterizes the uncertainty in the model parameters estimated from an ensemble of models . Correctly sampling from this distribution is therefore essential for accurate quantification of forecasted reservoir performance . The Neigbourhood algorithm utilizes the nearest neighbor property of the Voronoi cells, together with a Markov Chain Monte Carlo algorithm, in correctly sampling from the posterior probability distribution .
IntroductionPetroleum reservoir data is inherently uncertain . The field information is usually sparse and noisy . Part of the data is obtained from cores (-10-17 of the reservoir volume) collected at a finit e