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Fault-Displacement Studies |
1 Alastair Beach Associates, 11 Royal Exchange Square, Glasgow G1 3AJ, UK
2 GECO Exploration Services, Merlin House, Boundary Road, Working, Surrey, GU21 5BX, UK
This paper presents an interpretation of the geometry of normal faults in part of the offshore Nile Delta. The structure is dominated by north-dipping faults that are clearly imaged on seismic reflection profiles, and affect sediments of Pliocene-Pleistocene age, together with the underlying Miocene sequences that contain potential hydrocarbon reservoir rocks. The geometrical analysis is carried out in several stages. Firstly, time slice maps of the fault pattern are produced in order to establish the overall fault geometry of the area. Secondly, for each indivdiual fault identified, structure contours on the fault surface itself are mapped. This procedure serves to highlight any complexities in the geometry of the faults, and allows potential inconsistencies in the interpretation to be identified. Thirdly, horizon interpretations and correlations are made across the faults, and these are checked for consistency by constructing maps of the magnitude of the dip slip component of displacement within the fault surface. The complete geometric analysis makes it possible to extend the results from the good data areas in the upper parts of seismic sections to the poorer quality areas lower down. In this way it is possible to derive an interpretation of the structural geometry of the Miocene reservoir sequences. The seismic reflections from the Miocene are poor and irregular, and structural interpretation and modelling reduces the uncertainty associated with the reservoir geometry. The structural interpretation is presented as a model of tilted and fault bounded blocks, with considerable horizontal separation. This provides a much clearer and more consistent picture of the reservoir geometry, and contrasts with previous interpretations that have shown a more or less continuous reservoir sequence with little structure. The geometrical interpretation should form the basis for a new hydrocarbon play in the area because it predicts the locations of footwall crests, as well as areas where reservoir is missing because of separation across faults.
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