Abstract
Accurate information on fault networks, the full stress tensor, and pore fluid pressures are required for quantifying the stability of structure-bound hydrocarbon prospects, carbon dioxide sequestration, and drilling prolific and safe wells, particularly fluid injections wells. Such information also provides essential data for a proper understanding of superinduced seismicities associated with areas of intensive hydrocarbon exploration and solid minerals mining activities. Pressure and stress data constrained from wells and seismic data in the Northern Niger Delta Basin (NNDB), Nigeria, have been analysed in the framework of fault stability indices by varying the maximum horizontal stress direction from 0° to 90°, evaluated at depths of 2 km, 3.5 km and 4 km. We have used fault dips and azimuths interpreted from high resolution 3D seismic data to calculate the predisposition of faults to failures in three faulting regimes (normal, pseudo-strike-slip and pseudo-thrust). The weighty decrease in the fault stability at 3.5 km depth from 1.2 MPa to 0.55 MPa demonstrates a reduction of the fault strength by high magnitude overpressures. Pore fluid pressures > 50 MPa have tendencies to increase the risk of faults to failure in the study area. Statistical analysis of stability indices (SI) indicates faults dipping 50°–60°, 80°–90°, and azimuths ranging 100°–110° are most favourably oriented for failure to take place, and thus likely to favour migrations of fluids given appropriate pressure and stress conditions in the dominant normal faulting regime of the NNDB. A few of the locally assessed stability of faults show varying results across faulting regimes. However, the near similarities of some model-based results in the faulting regimes explain the stability of subsurface structures are greatly influenced by the maximum horizontal stress (SHmax) direction and magnitude of pore fluid pressures.
| Original language | English |
|---|---|
| Pages (from-to) | 227-243 |
| Number of pages | 27 |
| Journal | Tectonophysics |
| Volume | 699 |
| Early online date | 9 Feb 2017 |
| DOIs | |
| Publication status | Published - 15 Mar 2017 |
Bibliographical note
Some of the data used in this study have been published by Adewole and Healy (2013), among others. The authors especially acknowledge Professor David Macdonald for his invaluable contributions and co-supervising the research project. Our thanks are due to the Department of Petroleum Resources (DPR) and anonymous oil companies in Nigeria for giving permission to access some of the data for this study. E. O. A. also thanks Judith Christie, Clare Bond and other members of the Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen. We greatly appreciate the editor, and two anonymous reviewers for their critical assessments and vital comments, which tremendously improved the overall quality of the manuscript. Continuous supports on TrapTester software provided by Badleys, UK on the estimation of SI are much appreciated. The authors gratefully acknowledge the management of PCS Earth Techs Ltd. (Port Harcourt), Halliburton (Seisworks, ZMap and Stratworks), Kingdom, Rocdoc (Ikon science), EZ-ROSE, and CGG Veritas (Elog, Strata and AVO) for provisions of software and assistances.Keywords
- Niger Delta
- fault failure
- slip tendency
- fracture stability
- earth tremors