An uncertainty analysis study of the gas volumes in the field of Manati was conducted using gOcad™/Jacta™. The main uncertainties are associated to two important lateral limits of the reservoir, both ill-defined due to the poor quality 2D seismic lines available: the geometry of a major regional unconformity, and the Muta fault. A number of alternative realizations of the conjugated unconformity/Muta fault surface were generated, using four seismic interpretations. A p-Field-like algorithm was used to sample from a probability function locally taken as a trapezoidal pdf, defined by four sub parallel envelopes built from the four interpretations available. An artifice was conceived in order to overcome a deficiency of the software for dealing with multiple alternative lateral extensions of the model. This artifice consisted in modeling the grid with an extension taken as a maximum, and then computing only the volumes of interest by informing Jacta™ a number of alternative possible realizations of the unconformity/Muta fault surface, as if they where gas/oil contact scenarios. Accordingly, the real gas/water contact was given to Jacta™ as if it were an oil/water contact. Thus, with the corresponding fluid parameters informed in a coherent way, the gas volumes of interest where reported by Jacta™ as oil volumes. Other sources of uncertainty where taken into account by means of Jacta''s regular workflow.
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