1. A computer-implemented method for well surveillance comprising: defining, via a computer processor, a plurality of well attributes representative of well operating parameters; determining, via the processor, attribute statuses for each of the well attributes; defining, via the processor, a plurality of well performance classifications; mapping, via the processor, related ones of the well attributes into one or more of the well performance classifications; deriving, via the processor, well performance classification statuses for each of the well classifications, comprising the steps of (a) determining, for each of the well performance classifications, business rule values corresponding to the mapped well attributes, (b) assembling, for each of the well performance classifications, a well performance classification instance key comprising a combination of the business rule values, and (c) decoding, for each of the well performance classifications, the well performance classification instance key in accordance with a corresponding well performance classification decode key that assigns the well performance classification statuses based on the combination of the business rule values; and deriving, via the processor, an overall well status based on a combination of the well performance classification statuses, comprising the steps of (a) determining well performance classification status values representative of each of the well performance classification statuses, (b) assembling a surveillance instance key comprising a combination of the well performance classification status values, and (c) decoding the surveillance instance key in accordance with a corresponding surveillance decode key that assigns the overall well status based on the combination of the well performance classification status values.