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Fractures and Stress |
1 Schlumberger Exploration and Reservoir Services (UK) Ltd., Woodlands Drive, Kirkhill Industrial Estate, Dyce, Aberdeen, AB2 0ES, UK
2 Shell Petroleum Development Company of Nigeria Ltd., Freeman House, 21/22 Marina, P.M.B. 2418, Lagos, Nigeria
3 Schlumberger (Nigeria) Ltd., NRJ, c/o AFP, Batiment H, 50 Avenue Jean Jaures, B.P. 362, 92541 Montrouge, France
Modern 3D seismic techniques provide both high resolution and dense coverage for interpretation of subsurface structures, and are a great improvement on older 2D methods. Features at the lower limit of seismic resolution, however, are often not resolved and interpretation can be ambiguous. Structures at this scale, in particular small-scale faults, are critical for optimum placement of production wells and enhanced field development. Integration of structural analysis techniques from borehole dipmeter data with 3D seismic data allows re-examination of an interpretation and enhancement of such small-scale features.
Dipmeter analysis of a faulted structure in the Niger Delta has enhanced the structural model derived from 3D seismic. The faulted intervals were first identified using vertical dip trend analysis, and the faults were orientated by applying stereographic techniques to bedding dips in zones of fault-related deformation. Near-wellbore structure was then modelled by constructing dipmeter-based cross-sections using an interactive workstation, and minimum fault throw was estimated from these models. Accurate positioning of the faults on the seismic data was achieved by time-indexing the dipmeter log, and the structure was integrated with the present-day stress regime using borehole breakout analysis.
Application of these methods has allowed faults that were below seismic resolution to be identified and oriented, and for these to be explained in terms of the regional structural regime.
