ABSTRACT

Geoscientists often work on the edge of, or below the level of coherent seismic data. Large listric normal faults may be present in the poor data zone. If a proposed well crosses a large unknown growth fault, then an unexpected stratigraphic section is encountered. The result is confusion regarding the encountered geology.

On the Gulf of Mexico shelf, rollover structures form downthrown to listric growth faults. These rollover folds form as the hanging-wall geometry conforms to the shape of the footwall. Footwall geometry in turn determines fault shape. Thus, there is a causative relationship between the shape of the fault and the shape of the fold. This relationship allows industry to predict fault shape from rollover shape.

Often rollover structures are well imaged at shallow depths, but the image may deteriorate at greater depths. We present a graphical technique for projecting large growth faults to depth using the well-imaged portions of rollover structures. The technique, which is based on inclined shear collapse, is subject to measurement errors. Therefore, only two or three bends in a listric fault can be projected into poor data zones. In order to compare the theory to observation, we present constrained examples of projected fault surfaces using the well-imaged portions of Gulf of Mexico rollover structures.