Patent ID: 6801858
Filing Date: 2004-10-05
Classification: G01V

Abstract:
A method for facilitating identification of changes occurring, over time, in a physical state of a first zone of an underground formation, from changes detectable within a first time window of first sets of seismic traces respectively obtained during successive seismic surveys, by accounting for uncertainties of a number of seismic attributes, by accounting for uncertainties of a number of attributes, by reference to parts of traces of second sets of seismic traces recorded in at least a second time window corresponding to at least a second zone of the underground formation where the underground formation undergoes no significant physical state variation during successive sets of seismic traces, the method comprising:a) forming a learning base comprising physical states that have already been recognized and classified into categories, each physical state being defined by attributes of known statistical characteristics; b) obtaining uncertainties of the number of seismic attributes by statistical analysis of variations of seismic events of the second time window, the uncertainties being in a form of intervals of variable width expressing a lack of reproducibility of seismic attributes from one seismic survey to a next seismic survey of the second time window; c) constructing, an imprecise classification function in a form of probability intervals of variable width, using a discriminant analysis technique, and by reference to the learning base, the imprecise classification function allowing seismic events to be classified in the categories from available measurements based on the number of seismic attributes, while accounting for the uncertainties obtained by step b); and d) assigning each seismic event to at least one of the categories according to a width of the probability intervals.