Frictional Instability, Reactivation Tendency and Kinematic Feasibility of Crustal Faults in Extensional Niger Delta Basin, Nigeria

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Frictional Instability, Reactivation Tendency and Kinematic Feasibility of Crustal Faults in Extensional Niger Delta Basin, Nigeria

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Abstract

Faults compartmentalize reservoirs and their stability can be breached under the current stress field. Fault failure may result in stick-slip displacement releasing felt seismicity, reservoir seal breach leading to secondary fluids migration and contamination; wellbore and casing shear, associated fracturing and activation of new faults. In this paper, the structural attitudes of three representative faults have been measured from depth structure map and dynamically derived geomechanical characteristics determined at the depth point where the well intersect the fault planes. Fault instability and reactivation tendency was evaluated using Coulomb frictional and composite Coulomb - Griffith criteria; slip and dilation tendencies, instability factor and stress criticality. Results indicates that fault plane 1 dips at 0 0 0 0 0 20 and strikes at 068 , fault 2 dips at 40 , strikes at 299 while fault 3 strikes at 173 and dips at 09 . The principal stress 0 magnitude shows vertical stress of 87.5mPa, 84.3mPa and 84.6mPa, maximum horizontal stress of 52.7mPa, 62.8mPa and 59.5mPa; and minimum horizontal stress of 37.2mPa, 54.8mPa and 52.3mPa; while pore pressure was 17.4mPa, 11.2mPa and 13.6mPa and coefficient of static friction was 0.46, 0.43 and 0.44 on faults 1,2 and 3 respectively. The low coefficient of static friction is attributed to phyllosilicate asperities that smears and seals the fault surfaces. Fault plane 1 with the lowest failure stress of 3.34mPa also depicted an instability factor of 0.93 with a critical limiting stress of 3.54mPa is currently reactivating and undergoing aseismic creep and hydraulically conductive. Fault reactivation depicts the optimal orientation to be planes with poles between 78.1 and 36.7 parallel 0 0 to the maximum horizontal stress. Kinematically, stick slip displacement is infeasible because of the low dip angles of the gravitational faults and absence of a daylighting space. Reinforcement of the base by rollover anticlines and collapsed crest structures a common phenomenon in the gravitational faults of the basin is also a contributory factor for kinematic infeasibility hence faults critically stressed and optimally oriented for failure are undergoing aseismic slip and associated fault structural permeability enhancement.


Publication Info:

Author: Abija, F.A. , Abam, T.K.S. and Eze, C.L.

Volume: 57

Issue: September

Published By: Journal of Mining and Geology, 2024-09-01

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