Quick Look Techniques

Restored Tops

A restored top is an estimate of the depth that the top of a formation or marker would have had in a well, if it were not faulted out (Tearpock and Bischke, 1991). The use of restored tops can provide additional and critical points of control to improve the structural interpretation around a controlling fault.

The prospect map in Figure 1 was drawn without taking into account the restored tops for wells near the fault. The control for this interpretation is primarily downdip from the crest of the structure. In Figure 1, two drilling locations were proposed - one in the upthrown and the other in the downthrown fault block. The faulted out wells are the only wells that can provide additional data near the fault for the preparation of the map. Figure 2 was drawn after restoring the tops for those wells.

Fig. 1

Fig. 2

Notice that the interpretation changes significantly with the restored tops for Wells Nos. 3 and 11. The reserves for Reservoir C-3 are reduced by 46 percent and the reserves for Reservoir C-5 are reduced by 42 percent. In addition, the proposed well for Reservoir C-5 will be a dry hole.